It is known to use shirred tubular casings of synthetic, semi-synthetic or natural materials for packing food products, for example meat products in the form of sausage compositions or pieces of ham. These shirred casings, which are known in the trade as "sticks" or "hollow rods", are produced by gathering and longitudinally compressing long casings to a length which usually is only 1 to 3 percent of their original length. In order to fill a shirred casing with a sausage composition, in general, one end of the casing is first closed and then the casing is fit onto the stuffing horn of a sausage filling machine. The sausage composition is then forced under pressure through the stuffing horn into the casing which is thereby continuously unshirred. After a predetermined length of the sausage casing has been filled, cylindrical sausages are tied off and closed.
For various reasons, the diameter of the sausages should remain constant over their entire length. Optimum stuffing can be assured only by a uniform diameter of the casing, the size of which is, e.g., dependent upon the material used for the particular casing. If the casing is overstuffed, it may burst, whereas, if the casing is insufficiently filled, it will have a wrinkled surface.
Various devices for stuffing shirred tubular casings with sausage compositions have been proposed, which comprise special unshirring, smoothing and braking devices for achieving the most uniform diameter possible for the stuffed casings.
Thus, it is conventional to dispose, adjacent the outlet of the stuffing horn, a calibrating means, the outward surface of which presses against the inside wall of the casing to be filled and expands the casing. This contact pressure between the calibrating means and the inside wall of the casing gives rise to frictional forces which brake the motion of the casing (U.S. Pat. No. 2,871,508).
It is also known to package the shirred tubular casing together with a calibrating disk and to connect this assembly to the stuffing horn of a sausage machine prior to the filling operation (U.S. Pat. No. 4,007,761). The calibrating disk is surrounded by an unshirred portion of the casing, whereby the outer circumference of the calibrating disk should be larger than the internal circumference of the unshirred casing. During the filling operation, the casing is drawn over the calibrating disk and is thereby stretched and expanded (U.S. Pat. No. 4,077,090). The calibrating disk must be made of a rigid, inelastic material so that its diameter will not be altered by the contact pressure of the casing against the periphery of the calibrating disk. Braking of the casing as it is withdrawn from the shirred portion during the filling operation is effected by means of an additional device having the form of a ring with an annular attachment disposed following the calibrating disk whereby the braking effect is controlled by the frictional forces produced between the tubular casing and the attachment.
These inelastic calibrating disks have the disadvantage that the variations in casing circumference which cannot be avoided during the manufacturing process, will not allow optimum filling of the casing. Moreover, if the diameter of the casing is too small, there is danger that the casing may be damaged or torn by the calibrating disk. At the very least, an extraordinarily strong frictional force will arise between the calibrating disk and the casing, so that the casing will be overstuffed with sausage composition and have a tendency to be unable to withstand the high pressures which arise during boiling of the sausage, and burst. In addition, the degree of expansion of the sausage casing cannot be varied during the stuffing process, because it is predetermined by the calibrating disk used in each particular case.
Further, a calibrating device is known (U.S. Pat. No. 4,202,075) which is made of a flexible material and has a variable diameter. This device is also intended to stretch and expand the tubular casing prior to filling the casing with sausage composition and is designed for a controllable expansion, which, however, can be realized to a very limited degree only, depending upon the stretchability of the casing. Even with this device, however, strong frictional forces can occur between the tubular casing and the calibrating means. With this device, too, the braking of the tubular casing is effected using a braking element which is disposed ater the calibrating means and presses the tubular casing against the stuffing horn.